This invention relates to a dielectric filter having a configuration particularly suited for mounting it on a printed-circuit board. Such a dielectric filter can suitably be used for telecommunications equipment such as a portable telephone or mobile telephone.
FIGS. 1, 2 and 3 of the accompanying drawings illustrate a known interdigital tripole type dielectric filter comprising a substantially rectangularly parallelepipedic dielectric block 1 typically made of a ceramic material, through which a total of three holes 2a through 2c are bored from an end face to the opposite face. The through bores 2a through 2c are provided on the inner peripheral surface with respective internal conductors 3a through 3c, while an external conductor 4 is arranged on a lateral side of the dielectric block 1. Said oppositely disposed end faces of the dielectric block 1 carrying the openings of the through bores are divided into conductive short-circuiting surface sections 5a through 5c for electrically connecting respective ends of said internal conductors 3a through 3c and the external conductor 4 and open-circuiting surface sections 6a through 6c for electrically insulating the respective other ends of the inner conductors 3a through 3c from the external conductor 4, said surface sections 5a through 5c and 6a through 6c being interdigitally arranged in a manner as illustrated in FIGS. 1 and 2. A pair of L-shaped input/output terminals 7a and 7b are arranged on a side of the dielectric block 1 and electrically connected with the corresponding extreme through bores 2a and 2b via conductive holes 8a and 8b respectively and straight grooves 9a through 9d are formed on a pair of oppositely disposed sides or top and bottom sides of the dielectric block 1 between any two adjacent through bores, running in parallel with the through bores between said opposite end faces. The grooves 9a, 9c and 9d are arranged to regulate the degree of interstage coupling of the internal conductors 3a through 3c that operates as resonators.
The dielectric filter having a configuration as described above is then arranged on a printed-circuit board p as illustrated in FIG. 3 and soldered to the latter at m1 and m2, the input/output terminals 7a and 7b being respectively connected to input/output circuits s1 and s2.
For mounting such a conventional dielectric filter on a printed-circuit board p, as shown in FIG. 3, a suction pad t connected to a suction pump (not shown) is applied to the top (the side opposite to the one where the input/output terminals are arranged) of the dielectric filter to suspend the dielectric filter and move it onto the printed-circuit board until it is aligned with the input/output circuits of the circuit board, when the dielectric filter is released from the suction pad.
With such an arrangement, the suction pad needs to have a width equal to or smaller than the distance separating the two grooves 9c and 9d on the top of the dielectric block so that it may be brought to abut the narrow area between the two grooves to lift the dielectric block. This is because, if the suction pad t has a width greater than the distance between the grooves to cover the latter, air can easily come into the suction pad through the grooves to make it inoperative.
Thus, because of the relatively small effective area of the suction pad of a conventional system of mounting a dielectric filter on a printed-circuit board, the filter can drop from the suction pad to destroy itself by its own weight while it is being moved to the printed-circuit board and it is often difficult to place the suction pad precisely on the narrow inter-groove area of a dielectric filter.
It is therefore an object of the present invention to solve the above identified problems and thus to provide a dielectric filter that can be easily and securely mounted on a printed-circuit board.